Fiber having non-uniform composition and method for making same

ABSTRACT

A fiber having a non-uniform composition is disclosed. The fiber includes a first domain having a first composition and a second domain having a second composition different from the first composition. The fiber includes an interphase region intermediate the first and second domains that includes a blend of the first and second compositions to provide a gradual transition from the first domain composition to the second domain composition. A method for making such fibers is also disclosed.

RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/178,649, filed May 15, 2009, which is incorporated by reference inits entirety.

FIELD

The present disclosure is generally directed to fibers and moreparticularly to fibers having compositional domains positioned withinthe fiber to provide a non-uniform composition.

BACKGROUND

Functional fibers are used for a variety of different applicationsacross industries. In some cases the fibers are co-extruded bi-componentfibers, while in many others the fibers are monofilaments subsequentlyovercoated by a cladding of a different material to impart or enhancefunctionality. Exemplary such materials include polypropylene fiberscladded with antibiotics sometimes used for internal sutures andmicrowires cladded with doped sheaths for use in solar energyapplications.

Whether manufactured as a bi-component co-extruded device or asubsequently cladded filament, such fibers usually consist of twoconcentric polymer domains that oppose each other at an interface. Thereis, as a result, an abrupt change in composition between the domains ofthe two components. This in turn places limits on the functionality ofthe fibers and also the types of components that can be used to formsuch fibers.

These and other drawbacks are found in current fiber technologies.

It would be desirable to provide fibers and a method for making fibersin which multiple domains of differing compositions could be positionedadjacent one another to form a gradual transition between fibercomponents, thereby eliminating or ameliorating the effects of an abrupttransition between components at the interface.

It would also be desirable to provide fibers with multiple domains ofdiffering compositions in which the number and arrangement of three ormore components within the fiber can yield other advantages as a resultof the spacing and positioning of the domains with respect to oneanother within the fiber architecture.

SUMMARY

In an embodiment of the present disclosure, a multi-component fiber isprovided in which the components are arranged in at least three regionsor domains. In some embodiments, the domains are arranged such that thefiber contains a radially gradient composition. In other embodiments, amulti-component fiber is provided having at least three annular domainsin which the spacing and arrangement of the domains imparts afunctionality to the fiber. Attributes of the embodiments may becombined with one another such that the gradient composition itselfeffects the functionality of the fiber.

In accordance with these embodiments, a multi-component fiber spinningprocess is used to produce a commingled interpenetrating placement of aplurality of components through microfluidic extrusion. The resultantcommingled interpenetration defines an interphase, rather than aninterface. The interphase creates a designed region that can producegradient transition properties. The ability to create unique transitionsprovides the development of new architectures. In medical applications,for example, gradient transitions can be used to result in gradienterosion of the fiber.

In one embodiment, a fiber spinning apparatus having a four componentspinning head is used with four different source components to providedomains having up to fifteen different compositions from the variouscommingling of the four source components.

An advantage is that a radially non-uniform composition can be achievedin the fiber.

Another advantage is that a gradient composition can result intransition properties not otherwise readily achievable, if at all, infiber products.

Yet another advantage is that the compositional profile can further bevaried through the introduction of three or more components into thefiber.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a prior art bi-component fiber.

FIG. 2 shows a cross-section of a multi-component fiber having agradient composition in accordance with an exemplary embodiment of theinvention.

FIG. 3 schematically illustrates a partial cross-section of amulti-component fiber having a domain arrangement in accordance withanother exemplary embodiment of the invention.

FIG. 4 shows an exemplary spinning apparatus for use in making fibers inaccordance with exemplary embodiments of the invention.

FIG. 4 a shows an exemplary distribution plate for use in the apparatusof FIG. 4.

FIGS. 5 a and 5 b schematically illustrate static mixing of fibercomponents in accordance with an exemplary embodiment of the invention.

FIG. 6 shows an image of a cross-section of a multi-component fiber inaccordance with an exemplary embodiment having the domain arrangementillustrated in FIG. 3.

FIG. 7 shows the image of FIG. 6 under UV light.

FIGS. 8 and 9 show graphical representations of test results from thefiber shown in FIG. 6.

FIGS. 10 and 11 show graphical representations of test results fromanother fiber in accordance with an exemplary embodiment.

FIG. 12 shows an image of a cross-section of a multi-component fiber inaccordance with an exemplary embodiment.

Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

DETAILED DESCRIPTION

FIG. 1 illustrates a cross-section of a prior art bi-component fiber 5having a first, outer domain 100 (i.e., sheath) and a second, innerdomain 200 (i.e. core) which meet at an interface 20.

FIG. 2 illustrates a cross-section of a multi-component fiber 10 inaccordance with an exemplary embodiment of the invention. Asillustrated, the fiber 10 has five annular domains 100, 110, 120, 130,200, although as few as three and up to 15 or more may be provided. By“domain” is meant an identifiable region that can be distinguished fromadjacent regions. Although described and illustrated herein withreference to a fiber and domains having a circular cross-sectional area,it will be appreciated that the teachings herein are not so limited andthat the fiber and/or the domains contained therein may be of anydesired cross-sectional geometry.

Unlike the prior art bi-component fiber 5, which has two discretedomains and a single interface resulting in an abrupt transition betweenthe compositions of the two components that make up their respectivedomains, a multi-component fiber 10 of the present invention may providea gradual compositional transition between two components to establish agradient composition across one or more interphase regions 150. Theinterphase region 150 may be a series of closely spaced domains, totransition a change in composition across a radial distance, rather thanan abrupt change as would be experienced at an interface. Thus,exemplary embodiments having a radially gradient composition have acomposition that changes radially in a stepwise fashion across at leastthree domains.

In the illustrated embodiment, a core 200 and sheath 100 may each be adifferent component, such as those found in current bi-component fibers.A series of closely spaced intermediate domains 110, 120, 130 eachcomprise various combinations of the components used for the innermostand outermost domains (e.g., the core 200 and sheath 100). This allows agradient to be established in a stepwise or smooth manner that permits amore gradual transition from the outer composition to the innercomposition over a given radial distance. For example, if the inner-mostdomain (i.e. core) 200 has a composition of 100% of a component A andthe outer-most domain (i.e. sheath) 100 has a composition of 100% of acomponent B, the intermediate domains may be arranged to provide, againby way of example, a domain 110 that is 67% B and 33% A, a domain 120that is 50% B and 50% A and a domain 130 that is 33% B and 67% A (inwhich percentages are by weight percent). It will be appreciated thatthe innermost and outermost domains need not be 100% and that in certainembodiments, the domains illustrated in FIG. 2 as intermediate domain110 and 130 could be the inner or outer most domain, respectively.

By modifying the composition gradually over a radial distance throughthe use of an interphase region 150, an abrupt change between thecompositions of components A and B is avoided and one or more blendedcompositions of these components transition that change. This may permitmaterials to be incorporated together in a fiber that ordinarily couldnot be easily co-extruded with one another in a conventionalbi-component fiber, such as polyethylene terephthalate andpolypropylene, for example. The smoothness of the gradient may bemodified by the number of intermediate domains provided within theinterphase region 150 and the radial distance over which theintermediate domains 110, 120, 130 extend.

In one embodiment, each intermediate domain 110, 120, 130 of theinterphase region 150 has a thickness (measured radially) in the rangeof about 0.25 to about 50 microns, with the interphase region 150spanning a total radial distance in the range of about 0.25 to about 200microns. The intermediate domains 110, 120, 130 may, independently, spana radial distance equal to or different from one another. Furthermore,the intermediate domains 110, 120, 130 typically, but do notnecessarily, span a smaller radial distance than the core 200 and sheath100.

Fibers according to certain embodiments may have a total diameter in therange as small as about 5 to about 40 microns, and in some cases mayhave a total diameter in the range about 10 to about 15 microns, whilestill achieving spatially resolvable domains. In other embodiments, thefiber may have a diameter as large as 300 microns or even up to 1000microns depending upon the desired end use for which the fiber will beemployed.

The compositions used in forming the core 200 and sheath 100, and theblends of those materials used to form the interphase region 150 caninclude any suitable polymeric or other extrudable material depending onthe particular application for end use, including polypropylene andpolyethylene, by way of example only. Further, it will be appreciatedthat the intermediate domains are not restricted to blends of the coreand sheath components and that a third, fourth or greater number ofindependent components may be provided, for example, because ofparticular constituents which are desired to be embedded at variousradial distances within the fiber.

The resultant interpenetration and commingling of components in formingthe domains during fiber production may yield a fiber with finalproperties that are not achievable by the neat individual startingmaterials alone or in combination in a traditional bi-component fiberarrangement. Each component used in forming the core 200, sheath 100and/or the intermediate domains 110, 120, 130 of the interphase region150 may independently be a homopolymer, a co-polymer, or a blend of oneor more polymers and may further include one or more additives, such assurfactants, functional additives, and/or any conventional additivesused in fiber spinning that, for example, modify physical properties toaid in processing.

Surfactants may be provided as constituents in the compositions of thevarious components. For example, in some cases it may be desirable tofurther enhance the compatibility at the interface between domains ofcertain components, even where the compositional differences are lessabrupt, which the use of surfactants can help achieve.

Functional additives which may be incorporated into various componentsof the fiber in accordance with exemplary embodiments may depend on theend use for which the fiber is to be employed. It will be appreciatedthat in certain embodiments, the distinction between various componentsused in forming the fiber may be in the amount and/or type of aparticular additive. For example, a fiber may be formed from twocomponents, each of which are polypropylene-based, but in which thefirst component is neat polypropylene having no additives and the secondcomponent includes polypropylene and a functional additive, such as a UVfluorescent with an interphase region to transition a core of the firstcomponent to a sheath of the second component and establish a transitionin concentration of the fluorescent additive between these two domains.

The particular type of additive included in one or more of the fibercomponents and the loading of that additive in the component may dependupon the particular application for which the fiber is intended to beemployed. Multi-component fibers having a gradient composition may beuseful in crafting fiber architectures for many different end-useapplications including, but not limited to, the controlled bioerosion offibers in medical applications such as drug release, tissue engineering,and wound healing; smart fiber design (e.g. fibers containing materialsthat respond to chemistries of human activity, sensation or providefeedback response to environmental stimuli); optical waveguides;communications; applications involving the exchange of chemical andphysical energy between domains such as polymeric continuous solar fibersolar collection devices, environmental sensors, geotextiles;bioremedial applications; agrochemical delivery; veterinary drugdelivery and treatment; wound healing; bioengineering biomimetic tissueproperties; friend or foe textiles; and food security, all by way ofexample only. Thus, the type of additives included with one or morecomponents to be used within the fiber can vary widely and may includebioactive agents with chemistries such as extracellular matrixbiopolymers and tissue specific growth factors; tissue specificangiogenetic factors; rational and bio-derived active pharmaceuticals;chemotherapeutic agents; antibiotics; local and/or systemictherapeutics; as well as minerals and other inorganic growth materialsfor tissue engineering, wound care, wound healing, and reconstructiveprocedures used in other types of medical practice.

The use of two distinct domains 100, 200 and an interphase region 150 asa transition can be integrated into a more complex fiber architecturehaving multiple different or alternating domains with multipletransition regions between them and need not be limited to a transitionregion between a sheath and a core. Turning to FIG. 3, an example ofsuch an arrangement is schematically shown in which a four componentfiber is formed having components A through D in a plurality of domains,in which certain domains contain a single component, with a blend of twoor more components across a transition region between them.

In one embodiment, the four components are various blends of twopolymeric based compositions. The components may thus be selected sothat the fiber can be structured in such a way that an even smoothergradient is established between two discrete domains through aninterpenetrating network of commingled fibrils during fiber formation.For example, a first component (A) could be 100% of the firstcomposition, the second component (B) could be a 75/25 split of thefirst and second compositions, the third component (C) could be a 25/75split, with the fourth component (D) being 100% by weight of the secondcomposition. Thus, a domain provided as a blend of the first and secondcomponent (i.e., A+B) would result in a 87.5/12.5 split of the first andsecond compositions. In this manner, a gradient could be employed sothat the amount of the second composition increases as the radialdistance increases.

Alternatively, each of the components A-D may have compositions which donot include overlapping or a combination of compositions. In oneembodiment, each component is a composition that contains a polymerhaving at least one independent property (e.g. functional, chemical ormechanical) different with respect to each of the other three. Stillreferring to FIG. 3, polymer A may be selected for having apre-determined desired modulus, polymer B may be selected for having apre-determined desired elongation, polymer C may be selected for havinga pre-determined desired biological property and polymer D may beselected for having a pre-determined desired chemical activity. Throughcommingled placement of the four components to define a gradient (ormultiple gradients as illustrated in FIG. 3) the combined properties mayexceed the performance expectations of the individual materials extrudedas traditional single or bi-component fibers.

It will be appreciated that in embodiments in which more than twocomponents are provided, a gradient may still be established as a resultof changes in relative weight and/or volume percentages between two ormore components even if the weight percent of one or more othercomponents does not change from one domain to the next.

The fabrication of multi-component fibers in accordance with exemplaryembodiments of the invention may be performed using any suitable fiberspinning process and is preferably accomplished with a micro-extrusionfiber spinning process. In this type of process, a precision engineereddie defines intended domains as nano-fiber regions (i.e., fibrils) that,when combined at the spinning head, anneal into one single fiber havingany number of deliberately defined internal domains. Suitable devicesand methods for co-extruding a filament of different components in apre-determined spatial arrangement are described, for example, in U.S.Pat. Nos. 4,640,035; 5,162,074; 5,344,297; 5,466,410; 5,562,930;5,551,588; and 6,861,142 and in WO 2007/134192, all of which are hereinincorporated by reference in their entirety.

Preferably, the fiber spinning involves a high definitionmicro-extrusion process as described in WO 2007/134192. This process isa modification of fiber melt-flow spin extrusion adapted to produce aplurality of high definition geometric microstructures that arespatially resolved in cross-section. Spatial resolution may be obtainedeven in fibers having a diameter as low as about 5 to about 20 microns.

Referring to FIG. 4, a micro-extrusion apparatus 300 includes severalextruder barrels 310 that intersect into a die head 320. Each barrel 310delivers a single component for subsequent combination within the diehead 320. The die head is configured such that up to four, or in somecases up to eight, different polymeric components enter a series ofstacked distribution plates 330, together called a die-pack, in whichthe die plates have a series of predetermined openings and are orientedwith respect to one another to achieve a predetermined cross-sectionalarchitecture within the fiber. A unique die-pack may be provided foreach different fiber architecture.

According to one embodiment, four barrels 310, each containing adifferent polymeric component, feed into the die pack. The die packfacilitates spatial resolution, in which the molten polymers traversethe die pack in a defined tortuous path through the series ofdistribution plates 330 that result in a combination of vertical andlateral movements of a component to position a particular component at aparticular location within the cross-sectional area of the fiber toachieve a predetermined arrangement. There may be up to 64 stackeddistribution plates 330 per resolved cross-section.

Each extruder barrel 310 can provide a single component to the die pack.As a result, in a four barrel extruder set up using four differentcomponents, there are 4 factorial (4!) possible static comminglingcombinations; however, as a result of repeat combinations a singlecross-section can produce as many as 15 domains each having a differentcomposition based on various blends of the four components.

As better seen in the underside view of a distribution plate 330 shownin FIG. 4 a, each distribution plate 330 is a horizontal, lateral planethat consists of approximately 21,000 through-holes or microvias 337,which are arranged into approximately 5,250 four-hole, lateralchannel-units 335. Each microvia 337 forms a corner of a singlechannel-unit 335, with each microvia 337 contributing one microfluidicchannel to a center-point diagonal intersection of the includedrectangle of the unit 335. The intersection mixing point then flows downvertically to another four-via arrangement in the next distributionplate 330 directly below. The extent of vertical downward flow maydepend on the plate design.

Spatially resolved cross-sections and geometric designs are accomplishedby appropriately redirecting each channel through the orientation andarrangement of the succeeding distribution plate 330. In someembodiments, the final plate in the stack, which may be referred to as a“gradient plate,” can be used to manage domain resolution.

The polymer components emerge as fibrils from the gradient plate in thecommingled architecture as determined by the orientation of thedistribution plates 330. The fibrils are coalesced while still molten toform a single fiber having the desired cross-sectional architecture asdefined by the arrangement of the distribution plates 330 within the diepack. The formed fiber may then be wound, cut and/or spooled inaccordance with well-known fiber winding techniques for subsequent use.

In some embodiments, it may be desirable to cause a further, moreintimate mixing of the components after the desired architecture of thefibrils has been established through commingling, but prior tocoalescing into a single fiber. In these embodiments, a series of mixingplates may be placed in a mixing stack 340 that is part of the die pack.The mixing plates may be used to statically mix two or more adjacentfibrils by splitting and recombining them multiple times. Asschematically illustrated in FIG. 5 a, the mixing plates combine twoadjacent fibrils 510, 512 (having components 1 and 2) into a single flowchannel 520, which is then split into two separate flow channels 522,524 and recombined again. This process can be repeated several timesthrough subsequent mixing plates to generate the desired combination ofalternating components in the outgoing flow channel, as illustratedschematically in FIG. 5 b after one, two and three mixes.

The ability to place fibrils of different composition next to oneanother provides a form of solid state mixing in which the fibrils areintermingled by their placement within the cross-sectional architectureof the fiber, and which may be further enhanced through the use ofstatic mixing of those fibrils.

The proximity of fibrils of varying composition to one another presentsthe ability for the formation of interpenetrating networks, as fibrilsof a first composition become commingled with fibrils of a secondcomposition and a transition between domains is formed. Furthermore,surface energy characteristics of the various compositions of thefibrils when arranged in a commingled fashion to define the domains mayresult in a level of diffusion between those domains that furtherenhance the smoothness of the gradient across the radial distance of thefiber from one domain to the next.

In one embodiment, a fiber may be formed for medical and/or surgicalapplications that combines the enhanced strength found in certainmedical grade fiber materials with the degradation characteristics foundin biodegradable, but structurally weaker, fibers. By commingling suchmaterials in an interpenetrating network of fibrils to form a fiberhaving a cross section as shown, for example, in FIG. 2 or 3,biodegradation and/or biodissolution can be managed across a gradient toachieve a high strength fiber that will biodegrade or dissolve withinthe body at a controlled rate.

Exemplary materials for use in such embodiments, include providingpolypropylene or similar high strength material as the component for thecore 200 and a degradable polymer for the sheath 100 such aspolycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone,trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate,poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide,copolymers thereof, and combinations thereof. Varying combinations ofthe core and sheath materials may be provided as discrete intermediatedomains of the interphase region 150 to form the gradient as discussedpreviously, for example, with respect to FIG. 2.

In another embodiment, different or additional materials and/oradditives may be used to form medical fibers that can act as scaffoldsfor tissue engineering by, for example, incorporating medicaments and/ortissue growth promoters within certain intermediate domains. Thesematerials are released or revealed over time as a biodegradable sheatherodes away toward those intermediate domains which contain graduallydecreasing levels of biodegradable material and increasing levels of thetissue promoter. This can result in the grafting of cells to the fiber,resulting in its incorporation into surrounding tissue.

In still another embodiment, a conductive core is provided with p and npolymers commingled in alternating annular domains to form a fibercapable of collecting solar energy and converting and transferring thatenergy as an electrical charge. The conductive core can be used forelectron/energy collection of the charge flow created between thealternating n and p domains separated by a gradient transition region ina manner similar to that of infusion of n and p type silicon used inconventional solar applications.

The conductive core can be created using conductive polymeric materials,either as neat conductive polymer or as an enhanced and/or dopedconductive polymer with elements and/or molecular additives tofacilitate conductivity. Exemplary organic conductive polymers includepolyacetylenes, polypyroles, polythyophines, polyanalines,polythiophenes, poly p-phenylsulfide, poly(p-phenylene vinylene)s,polyindole, polypyrene, polycarbazole, polyazulene, polyazepine,polyfluorenes, and polynaphthalene. Certain undoped conjugated polymers,such as polythiophenes and polyacetylenes have a low electricalconductivity, but even at a low levels of doping (less than 1% byweight), electrical conductivity increases several orders of magnitude.In other embodiments, a conductive core can be produced by adding carbonblack or metallic materials as additives to an otherwise non-conductivepolymeric material, such as polyethylene.

The component used to form the n domain layer(s) can be any of thepolymers used to form the conductive core containing micronized n-typedopants such as tin, germanium, silicon, phosphorous, arsenic, antimony,and elemental complexes, while the same polymer containing dopants suchas boron, aluminum, or blue diamond, for example, can be used to formthe component for the p domain layer(s). n-Type domains supply highlevels of electron source while p-Type domains provide low electrondensity, such that a diffusion of electrons occurs from the region ofhigh electron concentration (the n-type side of the junction) into theregion of low electron concentration (p-type side of the junction);consequently, an n-to-p movement of electrons. The interdiffusion of then and p domains to facilitate this movement and the generation of anelectrical charge can be accomplished through the intermingling offibrils of the n- and p-type components to form an interphase regionthat blends n and p type domains as previously described.

It will further be appreciated that the designs shown in FIGS. 2 and 3are exemplary only and that any cross-sectional design in conjunctionwith any combination of two or more components employing an interphasetransition region 150 between those two components can be used, whichmay depend on the particular use for which the fiber is to be employed.

EXAMPLES

The invention is further described by way of the following example,which is presented by way of illustration of the concepts describedherein and is not intended to be limiting in any way.

In a first example, fibers having a cross-sectional diameter in therange of about 200 microns to about 250 microns were manufactured inaccordance with the schematic cross-sectional design shown in FIG. 3 toprovide gradual transitions from one phase to the next within thepolymeric composition of the fiber. The fiber was comprised of fourunique components designated as components A, B, C and D, each of whichwas fed from separate extruders into one spin head to produce a singlefiber.

Component A was polypropylene that had been pre-blended with carbonblack to provide a black appearance. Component B was polypropylenepre-blended with titanium dioxide and an organic UV fluorescing agent(Eastobrite OB1) to provide a white and UV responsive appearance.Component C was polypropylene pre-blended with carbon black and calciumcarbonate, selected to provide a black appearance to contrast the whiteand UV response of component B. Component D was polypropylenepre-blended with titanium dioxide to provide a white appearance.

The sample fiber was melt spun at 230° C. using an apparatus as shownand described with respect to FIG. 4 without the using of the mixingplates in which the four components were separated into six singlecomponent domains, consistent with the schematic shown in FIG. 3.Gradual transitions were formed between each single component domainsacross an interphase region having three interphase domains by blendingthe components across the interphase domains of that separating thesingle component domains. The annular transitional domains of theinterphase consisted of the component combinations as shown in FIG. 3.The fiber was collected and cross sectioned and examined analytically toverify the composition and determine whether the intended profile wasachieved.

FIG. 6 is a magnified image of a cross-section of the sample fiber,while FIG. 7 is a magnified image of the experimental fiber taken underUV light to confirm the presence of component B. An Energy DispersiveSpectroscopy (EDS) spectrum of the fiber cross section was taken at 100×magnification on a Hitachi S-3000N SEM equipped with iXRF EDS. Thesample was carbon coated in a coater supplied by Denton Vacuum tomitigate sample charging during mapping. A peak at 4.5 keV was measured,indicating the presence of titanium atoms and confirming the presence ofcomponents B & D.

FIG. 9 is an EDS map of a fiber cross section taken at 100×magnification, in which the dark spots indicate the presence oftitanium. FIG. 8 represents a line scan of spectroscopic data measuredhorizontally across the EDS map shown in FIG. 9; the general bell shapeof the spectrum is indicative of the gradient concentration of titanium.

A second example was prepared to produce a fiber in the same manner asin the previous example, except that mixing plates were incorporatedinto the die pack as shown in FIG. 4 to create a more intimate blend ofpolymers in the multi-component domains of the transition regionsbetween the single-component domains. In the second example, thecompositions of components A and B were switched (i.e., component A waspolypropylene pre-blended with titanium dioxide and the organic UVfluorescing agent and component B was polypropylene that had beenpre-blended with carbon black) to enhance the contrast in the studies.

This fiber was also collected and cross sectioned and examinedanalytically to verify the composition and determine whether theintended profile was achieved. FIGS. 10 and 11 illustrate an EDS map ofthe fiber cross section taken at 100× and 800× magnification,respectively. The dark spots within the map indicate the presence of thegradient distribution of titanium and confirmed that more intimatemixing was achieved. A magnified image of the cross-section of the fiberformed in the second example is shown in FIG. 12.

While the disclosure has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims.

1. A fiber having a radially non-uniform composition comprising: a firstdomain of a first composition; a second domain of a second compositiondifferent from the first composition; and an interphase regionintermediate the first domain and the second domain, the interphaseregion comprising a blend of the first composition and the secondcomposition.
 2. The fiber of claim 1, wherein the first domain forms afiber core and the second domain forms an annular sheath surrounding thecore, the interphase region annularly disposed intermediate the core andthe sheath.
 3. The fiber of claim 1, wherein the interphase region has athickness of about 0.25 microns to about 200 microns.
 4. The fiber ofclaim 1, wherein the interphase region comprises a plurality of annularinterphase domains in which each annular interphase domain has a weightratio of the first composition to the second composition that isdifferent from each domain directly adjacent thereto.
 5. The fiber ofclaim 4, wherein each annular interphase domain has a thickness of about0.25 microns to about 50 microns.
 6. The fiber of claim 1, wherein thefirst composition and the second composition comprise differentpolymers.
 7. The fiber of claim 1, wherein the first composition and thesecond composition comprise a same polymer.
 8. The fiber of claim 1,further comprising a third composition different from each of the firstand second compositions.
 9. The fiber of claim 1 comprising a coreforming an innermost domain, an annular sheath forming an outermostdomain, a middle domain intermediate the core and the sheath, a firstinterphase region intermediate the core and the middle domain, and asecond interphase region intermediate the middle domain and the sheath.10. The fiber of claim 1, wherein the first or second compositioncomprises a material selected from the group consisting ofpolycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone,trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate,poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide,copolymers thereof, and combinations thereof.
 11. The fiber of claim 1,wherein the first composition comprises a p-doped polymeric material andwherein the second composition comprises a n-doped polymeric material.12. The fiber of claim 1 having a diameter in the range of between about5 microns and about 300 microns.
 13. The fiber of claim 1 having adiameter in the range of between about 5 microns and about 20 microns.14. A fiber containing a radially gradient composition.
 15. The fiber ofclaim 14, wherein the radially gradient composition is defined by aplurality of discrete domains in which the weight ratio of a firstcomponent to a second component in each domain increases as the radialdistance increases.
 16. The fiber of claim 14, wherein the radiallygradient composition encompasses an interphase region of the fiberpositioned intermediate a central core and a sheath of the fiber. 17.The fiber of claim 14, wherein the radially gradient compositioncomprises a biodegradable material selected from the group consisting ofpolycaprolactone, poly-l-lactic acid, poly-d-lactic acid, polydioxanone,trimethylene carbonate, polyhydroxybutyrate, polyhydroxyvalerate,poly(FAD-SA), poly(CPP-SA), poly(FA-SA), poly(EAD-SA), poly glycolide,copolymers thereof, and combinations thereof, wherein the amount of thebiodegrable material in the fiber decreases along the radial distancefrom an outer surface to the center of the fiber.
 18. A methodcomprising: providing a first fiber component having a first compositionand a second fiber component having a second composition different fromthe first composition; extruding a plurality of fibrils from the fibercomponents; commingling the fibrils in a predetermined architecture; andcoalescing the fibrils to form a fiber having a radially non-uniformcomposition having a first domain comprising the first component, asecond domain comprising the second component, and an interphase regionpositioned intermediate the first and second domains and comprising ablend of the first and second components.
 19. The method of claim 18,wherein the interphase region is formed having a thickness in the rangeof about 0.25 microns to about 50 microns.
 20. The method of claim 18,wherein the interphase region comprises a plurality of annular domains.21. The method of claim 18, further comprising after the step ofcommingling but before the step of coalescing, statically mixing thecomposition of at least two fibrils.